The present invention relates to anti-tip devices for wheeled conveyances such as wheelchairs, wheeled conveyances including such anti-tip devices and more particularly to wheelchairs using such anti-tip devices that control forwards, sideways and backwards tipping and methods related thereto.
The wheelchair is one of the most important therapeutic devices in rehabilitation, as well as being a well known transportation appliance that enables an infirm, disabled and/or unwell person to move about with greater mobility than they would otherwise be able to do. A conventional wheelchair typically includes a frame, two rear wheels of large diameter and two forward wheels of smaller diameter, a seat and backrest. The seat and backrest are disposed on and secured to the frame so as to form a chair-like structure. The seat can be a padded seat, a solid seat, a sling seat or a seat comprised of webbing. The wheels, seat, and backrest typically are configured and arranged on the support frame so the greater part of the weight of the wheelchair occupant is resting on the rear wheels.
A number of studies have been performed concerning wheelchair safety. These studies have reported occurrences of acute injuries that were serious enough to cause the injured person to seek emergency medical attention and in some cases resulted in fatalities. Although there are a number of causes for such accidents, in a majority of cases the stability of the wheelchair, or the lack thereof, was a factor.
One very common hazard when using wheelchairs is that of tipping over backwards (i.e., rear-tipping accidents). Rear-tipping accidents typically occur when a wheelchair user leans backward, rapidly accelerates forward, wheels up an incline or strikes a low obstacle while wheeling backwards, particularly if the user""s center of mass is higher and farther back than usual, such as is the case with users who do not have legs. The reaction to the torque applied to the rear wheels provides a considerable tendency to tipping. When there is any additional factor such as going up a ramp, a hill or a curb, the risk of rear tipping increases further. Other tipping accidents include those in which the wheelchair tips forward or sideways.
As to rear-tipping accidents, many wheelchair manufacturers provide rear anti-tip devices to help limit the extent of rear tipping as an option for the wheelchair. These devices typically comprise rearwardly extending structures, with or without wheels, that prevent more than a minimal amount of rearward tilting. These structures, however, cause problems at the lower end of inclines much like scrapping the rear undercarriage of a car when starting up a steep driveway, in other words, they limit the departure angle of the wheelchair. Also, to the extent that such structures protrude beyond the rearmost aspect of the rear wheels, they tend to make the wheelchair unwieldly in close-quarters maneuvering such as in elevators, hallways, and with crowds of people. A low departure angle also prevents a wheelchair from being tipped back sufficiently to allow the front wheels or casters to clear obstacles such as curbs or so the wheelchair could be pushed over rough round. Such devices are shown for example in U.S. Pat. Nos. 3,848,883, 5,143,391 and 4,565,385.
In sum, to increase stability using such types of anti-tip devices, the device is designed so as to minimize or decrease the departure angle. When this is done, however, then the wheelchair becomes more unwieldly to use. As a result, the anti-tip devices are not used or are configured by the user in some cases so as to form some sort of compromise between stability and the usability or maneuverability of the wheelchair.
Other rear anti-tip devices have been developed that are only put into an operable condition upon some action by the user or by a third party. Until the anti-tip device is put into the operable condition, the device is not effective in minimizing or preventing the wheelchair from tipping over such as in a backwards or forward direction. When the anti-tip device is put into its operable condition, then the device either is subject to the same limitations of other rear anti-tip devices, as described hereinabove, or the operable condition of the anti-tip device effectively renders the wheelchair immobile. Examples of such devices are illustrated in U.S. Pat. Nos. 4,877,260, 5,181,733, 5,564,512, and 5,137,295.
It also is highly desirable for some wheelchair users to develop and master the skill of performing a wheelie when doing certain tasks. The wheelie is a highly useful skill that enables the wheelchair user, for example, to overcome a number of environmental obstacles such as climbing and descending curbs and ramps and turning in tight spaces.
With a conventional wheelchair, a wheelie involves the wheelchair user lifting the front wheels or casters off the floor so that the combined center of gravity of the user and the wheelchair (minus the rear wheels) is balanced over the rear axle. To xe2x80x9cpopxe2x80x9d a wheelie, the user accelerates the wheelchair forward while leaning backwards. The user maintains the wheelie by applying corrective forward and backward forces to the rear wheels with the hands or by shifting or altering body position.
Many users of conventional wheelchairs are leery of learning this skill, because of the large risk of completely tipping backwards and of striking one""s head on the floor, surface or an object, when performing or attempting to perform a wheelie. Also, many clinicians are reluctant to teach such a maneuver because of this risk. As a result, only a minority of wheelchair users do learn how to perform a wheelie.
As indicated above, to perform a wheelie, the wheelchair user must tilt the wheelchair backwards. However, the above-described rear anti-tip devices are configured so as to minimize the amount of rear tilting by the wheelchair. As such, a wheelie usually cannot be performed with a wheelchair that includes such anti-tip devices or structures. This is so because those devices or structures that maintain stability by limiting the departure angle, as a practical matter prevent a user from establishing the conditions needed for the user to xe2x80x9cpopxe2x80x9d a wheelie.
There is described in Physical Therapy, Volume 64, No. 5 an aid or device to assist training in balancing on the rear wheels of a wheelchair, what the article refers to as an advanced wheelchair skill and commonly known as a wheelie. The described device consists of two thick steel bars that are each bent in the form of a modified U. Each of the two ends of each bar is equipped with a screw collar clamp. Also, each bar is attached to the rear of the wheelchair by means of the screw clamp collars at two points, the rear upright and the tip bar of the wheelchair. In addition, small rollers are affixed to the terminal bend of each bar.
The article also acknowledges and identifies some shortcomings for the device. In addition to use-related shortcomings, the article provides that the device (i.e., the two bars comprising the device) presents a significant hazard to those walking behind the wheelchair and also increases the turning area required for the wheelchair. It is further provided therein that when the client has attained a certain level of proficiency and confidence the training aid or device is removed, thus the device has limited utility.
It thus would be desirable to provide an anti-tip device that would provide the desired stability to prevent or minimize the risk for completely tipping an apparatus such as a wheelchair in a rearwards direction, yet not result in a corresponding decrease in the maneuverability or usability of the apparatus or wheelchair. It also would be desirable to provide an anti-tip device that is easily adaptable for use to prevent or minimize the risk of tilting in at least one of a forward, rearward or sideways direction. It would be particularly desirable to provide such a device where the wheelchair user could regulate the maximum amount of tilting that is to be allowed as well as a device in which the mechanism for increasing stability and regulating tilting is self-actuating. Further, it would be desirable to provide an anti-tip device that would allow a user to xe2x80x9cpopxe2x80x9d a wheelie at any time and yet protect the user from excessive rear tilting during such maneuvers as well as at any other time. It also would be desirable to provide such a device that would increase the maneuverability of the wheelchair as compared to wheelchairs configured with prior art anti-tip devices. Anti-tip devices of the present invention preferably would be simple in construction as compared to prior art devices and would not require highly skilled users to utilize the device.
The present invention features an anti-tip device for regulating the amount of allowable tilting for an apparatus, such as a wheeled conveyance including a wheelchair, in one of a backward, forward or sideways direction. Also featured is such an anti-tip device in combination with a wheeled conveyance and more particularly, a wheelchair including such an anti-tip device. Such an anti-tip device is advantageously configured so it automatically deploys from its stored or rest position into an operable position responsive to the tilting motion of the apparatus or wheeled conveyance in the direction to be regulated.
Such an anti-tip device, when used in conjunction with a wheelchair, also advantageously minimizes the risk of a wheelchair user overturning the wheelchair while not otherwise causing an interference or impediment to the maneuverability of the wheelchair. Further, such a device advantageously allows a user to xe2x80x9cpopxe2x80x9d a wheelie at any time and still minimizes the risk to the user of overturning the wheelchair in a backwards direction while performing the wheelie or at any other time.
In addition, such an anti-tip device allows a wheelchair user to tilt the wheelchair backwards so the user is supported by the anti-tip device, preferably two such devices, and the wheelchair rear wheels. Such a condition or operational position of the wheelchair is hereinafter referred to as a xe2x80x9cwheelie+xe2x80x9d. This rear-tilted arrangement of the wheelie+ is advantageous because it may be helpful in reducing postural neck strain from looking up to make eye contact with a standing person(s). The wheelie+ position also may be helpful in reducing the likelihood of pressure sores caused by sitting upright for long periods of time. Wheelchair users can use the wheelie+ to achieve most of the benefits of a conventional wheelie in overcoming obstacles. The wheelie+ is much easier for users to learn than the conventional wheelie.
In a first aspect of the present invention, the anti-tip device includes a housing that is secured to the frame or support structure of an apparatus such as a wheel-chair or other wheeled conveyance, in which housing is rotatably secured a support arm. The housing is configured so the support arm is in either a rest position or an operable position. The rest position generally corresponds to the non-tilted condition of the apparatus such as the upright position of a wheelchair. When in the operable position, the housing engages the support arm so as to prevent further rotation of the support arm with respect to the housing.
When the apparatus is tilted in one of a backwards, forward or sideways direction, the support arm rotates within the housing out of the rest position responsive to this tilting of the apparatus. When the apparatus tilts a predetermined amount, the support arm is rotated so it is in the operable position. In the operable position, a distal end of the support arm is in contact with a support surface, such as a floor. Thus, the engagement of the support arm with the housing when in the operable position coupled with the distal end being in contact with the support surface thereby prevents further tilting of the apparatus. Thus, the maximum amount of tilting that is to be allowed for the apparatus is regulated by the amount of rotation by the support arm into the operable position.
More specifically, when the apparatus is tilted a first amount, an amount less than that required to place the support arm in the operable position, the distal end of the support arm comes into contact with the support surface. As the apparatus is tilted further the support arm continues to rotate within the housing until the support arm engages a portion of the housing thereby stopping further rotation and thus putting the support arm in the operable position.
In specific embodiments, the housing of the anti-tip device further includes a tilt-adjusting mechanism that selectively adjusts (i.e., increases or decreases) the angular distance between the rest position and the operable position. Adjusting this angular distance correspondingly regulates the amount of tilting. For example, if the angular distance is increased, the support arm can rotate through a longer arc and thus increase the maximum amount of tilting that can be achieved by the apparatus. Similarly, if the angular distance is decreased, then the support arm rotates through a smaller arc and thus the maximum amount of allowable tilting is thereby decreased.
In a first embodiment of the anti-tip device, the adjusting mechanism comprises a cam that is rotatably mounted with the housing so a surface thereof contacts a surface of the support arm when it is in the operable position. Additionally, the adjusting mechanism includes a rotating mechanism, to which a cam is secured thereto, to selectively rotate the cam. In this way, a selected one of a plurality of cam surfaces is rotated into a position so the selected cam surface contacts the support arm surface when the arm is in the operable position. Thus, a user can adjust or regulate the amount of angular rotation (i.e., arc length) by the support arm between the rest position and the operable position and thus regulate the maximum amount of tilting.
In a second embodiment, the anti-tip device includes a pin member and the sides of the housing include a plurality of through apertures that are arranged so as to form a plurality of pairs of such apertures, where the pin member is selectively received and removably secured in one of the pairs of plurality of through apertures. The pairs of through apertures in conjunction with the pin member comprises another means for adjusting the angular distance of rotation for the support arm between the rest and operable positions.
In a third embodiment of the anti-tip device, the housing includes a threaded aperture positioned so one end thereof faces the area in which the support arm rotates within the housing. A threaded member is threadably received within the threaded aperture and is inserted therein such that one end thereof extends beyond the end of the through aperture facing the support arm. The threaded aperture in conjunction with the threaded member comprises another means for adjusting the angular distance of rotation for the support arm between the rest and operable positions.
In a second aspect of the invention, there is featured a wheelchair including at least one such an anti-tip device and preferably a plurality of such devices to regulate the maximum amount of allowable tilting the wheelchair can achieve in one of a forward, sideways or rearward direction.
In a third aspect of the invention, there is featured a wheeled conveyance having at least one rear wheel and a support frame in combination with an anti-tip device according to the present invention that regulates the maximum amount of allowable tilting the wheeled conveyance can achieve. The wheeled conveyances include but are not limited to unicycles, bicycles, tricycles and un-powered or powered vehicles having four or more wheels.
In a fourth aspect of the present invention, the distal end of the support arm is configured so a wheel or another type of rotating member extends therefrom. Thus, for example, a wheelchair user can easily move the wheelchair about in the wheelie+ position even though the wheelchair is tilted backwards and the support arm deployed in the operable position where the wheel at the distal end is in contact with the support surface. In particular embodiments, the wheel at the distal end is castered or otherwise configured so it can swivel about a vertical axis at the support arm distal end for increased mobility. In particular, the wheel at the distal end is configured so the wheelchair user can pivot the wheelchair about an axis generally perpendicular to the support surface even though the wheelchair and the user are being supported by the extended wheel of the anti-tip device and the wheelchair rear wheels.
Alternatively, the support arm distal end is configured so as to include a plurality of wheels. The distal end also can be configured so as to include a secondary support structure for the plurality of wheels. For example the distal end can be configured with U shaped structure to which the plurality of wheel are rotatably, and preferably swively, mounted.
Other aspects and embodiments of the invention are discussed below.